Radio signaling system



'Max'. 3. 1925.

c. s. DEMAREsT ET Al.

RADIO SIGNALING SYSTEM Filed D80. 31, 1923 2 Sheets-Sheet 1 1N VEN TORSA TTORNE Y Mar. 3. 19.25.

c. s. DEMAREST ET Al.

RADIO SIGNALING SYSTEM 1 Filed DeC 51'. 1923h 2 Sheets-Sheet 2 am W. 4www 4 \M.|||I F e s.

A Si! WW 1 M n A u N ATTORNEY Patented Mar. 3, 1925.

UNITED ,STATES PATENT OFFICE.;

CHARLES S. DEMAREST, OF RIDGEWOOD, JERSEY, AND MILTON L. ALMQUIS'T, OF

BROOKLYN, `NEW YORK, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPHCOMPANY, A CORPORATION 0F NEW YORK.

RADIO SIGNALING SYSTEM.

Application med December 31, 1923.A Serial No. 638,748.

To all whom t 'may concern."

Be it known that we, CHARLES S. DEMA- REsT and MILTON L. ALMQUTST,residing at Ridgewood and Brooklyn,in the counties of Bergen and Kingsand Statesv of New Jersey and New York, respectively, have inventedcertain Improvements in Radio Signaliner Systems, of which the followingis a speci cation.

This invention relates to radio signaling systems, and particularly tomeans for selectively signaling a particular station ofl such a system.

In the operation of a multi-station system, it is, of course, desirablethat each station of the system shall be able'not only to.

paratus is designed. This will care for slight variations of ,thecalling frequency sent from another station. of frequencies should notbe too great else the apparatus will res ond to frequencies not intendedfor the ca ling of the stations of the system. In' the copendingapplicationrof Demarest and Almquist, Serial No. 646,903, filed June 21,1923, is described a method and ineans for the transmission of a callingsignal from one station to another of a multi-station system in whichthe high frequency carrier current is modulated by impulses of currentof 135 cycles in accordance with a definite code and transmitted. At theparticular station called, the modulated hi h frequency current isdemodulated, an the impulses of 135 cycle current serve to Voperate arelay kresponsive to this frequency. While, of course, the relay may" bemade to respond to other frequencies within a range extending, forexample,

from 130 to 140 cycles, it 1s, of course, de-

'sirable to make the range as narrow as possible in order to prevent theoperation of `other station of the system.

But therangethis relay by currents other'than the calling signalingcurrents transmitted from an- Any method, therefore, by which thesensitivity of the receiving set at 1'35 cycles may be increased will beof value. y

One of the objects of this invention is to increase the sensitivityofthe receiving sets for calling signals, which object is obtainedeither by using a separate receiving set for the calling signals fromthat used in the reception of speech signals (each set being of maximumefficiency for the respective range of frequencies) or by usingdifferent connectons in a receiving set designed for the joint receptionof the calling and speech signals, the lsaid receiving sets beingdesigned to take advantage of certain conditions inherent in thereception of a particular low frequency signal.

A low frequency signaling system, such as the 135 cycle system referredto above, has the advantage that the'frequency of the s'de band is veryclose, to that ofthe carrier and therefore higher regeneration may beemployed than is possible for speech reception (where the side band isfairly broad), the "regeneration being carried to a point very close tothe oscillating condition.

AThis makes is possible to obtain maximum amplification through the useof the minimum number of vacuum tubes. The regeneration may be obtained-by plateand gridv tuning or by a magnetic feed-back as in the ordinaryregenerative circuit. Since the increase in regeneration increases thesharpness of tunin and since the signaling apparatus, that 1s, the callresponsive apparat-us, must be able to function at all times, it becomesnecessary to keep the wave length of the transmitting station withinnarrow limits. A. device for controlling the trans-` mitted carrierfrequency is shown in the copendin ap lication of yDemarest andAlmquist,eria No. 646,903, led June 21, 1923.

The present invention 1s concerned mainly nection with the attacheddrawing, of which -A Figure 1 shows an embodiment of the invention inwhich a single radio receiver functions for the detection of both thespeech and the callingsignal, and Fig. 2 is a form in which separatereceiving circuits have been' provided for the speech and the callingsignals, each of which is highly etlicient vfor the particulai`frequencies employed. f

-In Fig. 1, which represents two stations A and B of a multi-stationsystem, the transmitting antenna 1 at station A has connected therewitha radio transmitter 2, which may be of any well-known type, by means ofwhich a carrier current may be modulated by speech currents and also bycalling signal currents, and the resultant modulated waves may betransmitted to the other stations of the system. At station B thereceiving antenna 3 is connected with the radio receiver 4 by means ofthe coupling transformer 5. The secondary winding of this transformer isconnected with the grid and filament of the vacuum tube detector 7 theinput circuit \including the condenser 6 whereby the input circuit maybe tuned broadly to cover the range of frequencies to be received atstation B and also including preferabl a grid condenser and leak. Theoutput side of the detector 7, viz., the platelilam nt circuit, includesan inductance 8 whichis arranged dbe shunted by the operation of therelay 20. This'output circuit isconnected with the armatures of relay10, the outer contacts of which extend to the calling-signal amplifier11 and the innerV contacts of which extend to the speech-sigamplifier15. The vacuum tube 13 of the amplifier 11 is connected `with the outputof the detector 7 by means of the transformer 12. The condenser 9 is-ofsuch value relative to the primary 'Winding of transformer `512 as`totune the circuit for 135 cycles so that the maximum gain will be atthis frequency. The output side of the tube 13 is connected with thecalling-signal apparatus 14, which may be either of the type disclosedinthe copending ap lication of Demarest and Almquist,'Ser1al,No.646,903, cited heretofore,'or of any well-known type. The outvput sideof the detector 7 is connected with the vacuum tube 17 of thespeech-signalA amplifier by means of the transformer 16, and the outputside of the tube 17 is connected with the telephone receiver orequivalent d evice 18. Relays '10 and 20 yare connected with thesource-of current 21 and also with the receiver switchhook 19 in suchmanner that when the receiver 18` is upon the hook the circuit of therelays is open and remains deener 'zed until the receiver 18 is removedfrom t e hook of the switch v19. Battery 22 serves to provide thelilament heating current for all the vacuum tubes, and battery 23provides the plate current for/tubes 7 'and lor the transmission ofspeech and calling signals from station B to other stations,

frSuch as A, of the radio system, a transmitting antenna 27 is providedhaving connectedV therewith .a radio transmitterI 26, which may be ofthe type represented by 2 of station A. Similarly at' station A areceivingantenna 28 having a radio receiver 29 connected therewith isprovided, which radio receiver should preferably be similar to thatrepresented by 4 of station B.

Having in mind the foregoing description of the parts of theapparat-usin which this invention is embodied, it will be clearlyunderstood from the following description of the method ,of transmittingcalling and speech signals, for example, from station A to station B.'Let it be assumed that a wave be transmitted from antenna 1' comprisinga carrier and its side bands representing 'the carrier as modulated-by1-35 cycley current. This modulated wave might be transmitted inaccordance with a code in the manner described in the copendingapplication of Demarest and Almquist, Serial No. 646,903, or might be anuncodedsignal. In any case the carrier and the side band would bereceived by antenna 3 Iand impressed by the transformer 5 upon the inputcircuit of the detector 7. The 135 cycle current resulting fromdetection would be impressed by the output circuit of the detector 7upon the signal frequency amplifier 11. The 135 cycle current asamplified` by 11 would be impressed upon thecalling signal apparatus 14,and the operation of this' device would apprise the subscriber atstation B that another station of the system desired to get incommunication with him. -As pointed out heretofore, the inductance 78 inthe output side of the receiver 4 is adjusted to tune the plate circuitto the point where it will almost oscillate at the radio frequency forwhich the set is tuned. By such adjustment,

the radio receiver is made highly regenery ative, thereby giving highamplification to frequencies'c'lose tothe carrier, such for example, asthe frequencies obtained whenthe carrier is modulated by 135 cycles. Inthis manner, andalso by the use of an amplifier 11, which gives maximumamplication at 135 cycles, the receiving eiciency of station B at the fruency of 135 cycles is materially improved. eqUpon the receipt -of thecalling signal .at B, the subscriber removes his receiver 18 from thehook switch 19 which completes the circuit from battery 21 through relas 20 and 10 and thereby operates these re ays. y lay 20, the inductance8 is shunted and thereby effectively disconnected from theoutput-circuit of the detector 7. This actA detunes the output circuitof thedetector By the operation of re- -relay 10,

and decreases the re eneration'fto a point quencies connected with voicerange, that is, 2 00 to 2,00Q`cycles.-

The arrangement shown in Fig. 2'rep'resents a system in whichseparatefradio ,ref ceivers are provided orfthe speech recep-' tioncircuit and .for the signal reception cir-- cuit. In this ligure,transmitting antenna 40 and radio `1 :ransmitter-4J. correspondfto theelements designated 1 and 2.0i Fignl. At station B receivin'g antenna 42isv lcon'-l .nected vwith the armatures" .of -relay's 43.

This antenna snormally connected with the signal reception circuitthrough.l the outer contacts of the said' relay. The `inner contacts `ofthis -relayserveto' connect' the antenna with the speech receptioncirc1'1it.- y A tuning condenser' 45 and a primary 'winding 46 oftransformer '47 are connected meansv 'of conductors v44 and theoutercontacts ofy relay 43 with the antenna 42 in order to tune contains a 35the antennal for thefrequencies of thecalling signal. The secondary 48of transformer47 is connected withjthe-'input'side of the vacuum tubedetector' 50, andthe condenser 49'is connected across lthewindine'gj 48in order to tune this circuit to the incoming The output side ofthegtube40 feed-back winding. 51 in order to provide for 'regeneraton, and thecir-v cuit also contains the, rimary winding 52 frequency,

of transformer where y'tbezdetected com. ponent, that is, the 135 cyclecurrent, will. be impressed vupon the input of the vacuum tube amplifier57 by the transformer winding 54. The-primary winding 52 of trans former53-'is tuned' to 135cycles"by the vconv l incoming high frequencycurrents as modulatv denser 58. The-output'circuitf of this tube-contains the primary-windingp) of trans# 'former 60, of which thesecondary winding 61`is connectedwit'h the-.signaling apparaf ftus-62'responfsi've tothe amplified 135'l cycle.

j The speech reception'sl'cii'cuitjincludes at lits input end the tuningcondenser 69 1and .the primary winding 700i transformer 71 f whereby theantenna.- 42 may be.

' lthe particular range of currents'represented Pliner-represented bythetube,v connecting circuit, a detector represented by the tube and itsconnecting-circuit, and .anv audiofrequency 'ampliiierrepresented e.

t" tuned antenna circuit is connected with the t vsideof tube74 by meansof the-trans- -former 71, `the colmection including thesecondarywi'nding 72 and theituning' `condenser the` speech frequencies.kv'Tliespeech Fre cep" the carrier tion circuit comprises a radio thetube 84y and its :connecting circuit.

v signal transmitte yed by the speech" by the high frequency amplifierA74 and will detector frequency' asf-modglgtgsl by i,

' plicantsinvention.

tube 84 the output side of which is connected bymeans of windings 85 and87 of transformer with the telephone receiver 88 is tobe `understoodthat common sources of current supply might beused in place .of theseparate'sources shown on the drawing. Re lays 43 and 90, havingconnected therewith battery 91,l are designed to operate when ception`circuit. The loperation of relay. 90

vserves to connect the source of current- 98 With the filaments of thevarious vacuum'.

tubes in orderto energize the tubes.V

The output side of the detector is con- [nected by means ofthe windings81 and 83 "of transformer 82 with the input side of the receiver 88.fisremoved from the switch- -hook 89. -Upon the operationof relay 43 *theantenna 42 will be connected by conduc- "tor 68 withthe input vside ofthe speech re` Since the signal reception circuit is norl mallyconnected by means -o conductors 44 with the receivin `tion- A will beimpressedbyv the'tran'sformer antenna 42, the calling from antenna'40atsta- 47 upon the detector 50 which is designed to be regenerative., Thedetected-currents willbe impressed by transformerf53 upon,

the 135 cycle amplifier circuit,which is also designed to'givehigh'amplication at this particular frequency. The low lfre uencyI 00,

component will beimpressedby trans ormer '60 upon the signalingapparatus 62.` U on the receipt'of 'a calling-signal, the subscri erlat'station B removes 'his receiver 88 from .the hook of switch .89which operates relays 43 and 90 thereby connectingtheA antenna 42 V withthe speech reception circuit and also ener'gizing the vacuum tubes ofthe circuit. The

'ampliier and the resultant amplified hown at station B. f y

1- ngshould 2also 'bec-undergrad um time' 4w'ehave' shcwn only twostations, vthere are representatlve jofi lany z number g of stations'While this invention embodied in 'a particular vform, it`s` to be;

in other and different forms without departing from the spirit of theinvention as defined in the appended claims.

lVhat is claimed is:

1. In a radio communication system, the combination with an antennaadjusted for the reception of a plurality ofiy bands of frequencies, ofa radio receiver connected with the said antenna and comprising a vacuumtube detector having its output circuit so tuned that it will almostoscillate when.

the frequencies of one of the said bands are applied to the Saiddetector, an amplifier connected with the said receiver adjusted to givemaximum amplification to one of the frequencies resulting fromdetection, and lan indicating device responsive to the low frequency.

2. In a radio communication system, the combination with an antennaadjusted for the reception of a plurality of bands of frequencies of aradio receiver containing a vacuum tube detector having its input cir-v4cuit connected with 'the said antenna and having its output circuitnormally connected with an amplifier designed to give maximumamplification of one of the said bands, a second amplifier designed toproduce maximum amplificationof another band of frequencies andswitching means to connect the said radio receiver with either of saidampliers.

3. In a radio communication system, the combination with a broadly tunedantenna of a radio receiver connected with the said antenna andcontaining -a vacuum tube detector whose input circuitv is ,tuned tocover the same range as the said antenna and whose output circuit isnormally connected with an` amplifier designed for maximum amplificationof certain of the received frequencies, the said output circuit beingnormally tuned to almost oscillate at the received carrier frequency,and switching means to detune the said output circuit` and to disconnectit from the said amplifier.

4. In a radio communication system, the

other frequencies received by said antenna,

and switching means to disconnect the' said output circuit from the saidfirst amplifier and to connect it with the said second ampliier and alsoto detune the said output circuit.`

5. kIn a radio communication system, the combination with a transmittingstation arwaves vand valso signal-modulated carrier waves, of areceiving station having an antenna tuned for the reception of both ofsaid waves, a detect-or connected Ywith the said antenna,\a plurality ofreceiving circuits each designed for maximum eciency throughout therange of frequencies which each is intended to receive, and switchingmeans to control the connection of the detector with each of the saidreceiving circuits.'

6. In a radio receiving System, the combination with an antenna of avacuum tube detecting circuit connected therewith having its plate andgrid circuits tuned almost to ranged to transmit speechvmodulatedcarrier Y the oscillating state for the received carrier r."fiequency, asignal amplifying circuit. a speech amplifying circuit, and switchingmeans `to connect either of said amplifying circuits to the saiddetector.

In testimony whereof, we have signed our.

namesto thisv specication this 29th day of December, 1923.

CHARLES s. DEMAREST. MrL'roN L. ALMQUIST.

